dart2js: use WorldImpact for dump_info

pkg/compiler/lib/src/enqueue.dart

Index: pkg/compiler/lib/src/enqueue.dart
diff --git a/pkg/compiler/lib/src/enqueue.dart b/pkg/compiler/lib/src/enqueue.dart
index 2fef15ca51747063da26d524ccd0679786aa8824..53796dc0280bd5b91654605cabf17610745d66ce 100644
--- a/pkg/compiler/lib/src/enqueue.dart
+++ b/pkg/compiler/lib/src/enqueue.dart
@@ -888,8 +888,7 @@ class ResolutionEnqueuer extends Enqueuer {
 /// [Enqueuer] which is specific to code generation.
 class CodegenEnqueuer extends Enqueuer {
   final Queue<CodegenWorkItem> queue;
-  final Map<Element, js.Expression> generatedCode =
-      new Map<Element, js.Expression>();
+  final Map<Element, js.Expression> generatedCode = <Element, js.Expression>{};
 
   final Set<Element> newlyEnqueuedElements;